Irradiation of sodium base greases



United States Patent invention relates to lubricating grease compositions, and more particularly to a process of improving 1certain physicalproperties of sodium base lubricating greases. I In brief compass, the invention pertains to subjecting sodium base'lubr-icating greases to high intensity ionizing-radiation to 'obtain greases having-color and odor improvement as well .as other desirable grease char- .acteristics. i

In the prior art, improved physical properties'of lubrieating greases have usually been'attained through the use I of special refining or finishing methods, unique thickening agents or oil bases and particular additves. In accordance with the present invention, it has now been found that physical properties of sodium base lubricating greases can be markedly improved by irradiation of the greases with high intensity ionizing radiation comprising gamma rays. .This .process has the advantages that usually it is less expensive than the prior art methods, it is more easily controlled, and it is more readily adapted to a continu- 0.11s operation.

The gamma rays with which the lubricating greases of the invention are irradiated may be derived from the radioactive decayof certain natural or artificially radioactive elements or isotopes such as radium 226, radium A,- radium B, radium C, radium D, thallium 210, cobalt 60, cesium 137, europiurn 152 -154,'cesium 134, cerium 144, silver 110, thulium 170, tantalum 182, scandium 46, terbi um 16 or iridium 192 or from chemical compounds of or materials containing such elements or isotopes. The gamma-rays may also be derived from suitably shielded radiation produced in nuclear reactors, i.e. atomic piles, or from the spent fuel elements obtained from the operation of such reactors.

In general, undisturbed gamma ray fluxes within the range of about 10 to 6x10 usually about 10 to 3 X103,

roentgens per hour, such as that derived from a cobalt 60 source, will be employed in irradiating the sodium base lubricating greases. The time of irradiation will depend -uponthedegree of change in the physical properties of the lubricating greases desired as well as upon the radiation dosage rate. The total radiation dosage (based on undisturbed radiation field conditions, i.e. conditions prior to the introduction of the lubricating oil into the radiation field) will ordinarily be within the range of about 10 to 3x10 preferably about to 3x10 roentgens of gamma rays. Thus, irradiation time may vary from about 0.01 to 3000 hours, preferably about 0.5 to200 hours.

i For the purposes of this invention, however, the lubricating grease need only be irradiated for a sufiicient period of time, to obtain the desired change in physical properties.

' The sodium base greases may also be irradiated in an atomic pile wherein the radiation will consist primarily of fast and slo w neutrons and. gamma rays.

The lubricating greases employed in the invention may be anyof the sodium soap thickened greases described in chapter 11 of Boners Manufacture and Application of Lubricating Greases? (Reinhold Publishing Corp.).

iberfswithin the range. of about 0 to'154 havihg Patented June 27, 1961 jbout 12 to 30, preferably aboutlS to 22; carbon 'atom sff'per molecule, such as lauric, myristic, palmitic, steari'c'ffl2- hydroxy stearic, 9,10-dihydroxy stearic, behenic, myristoleic, palmitoleic, oleic, linoleicalig'noceric, ricinoleic and erucic acids,'cottonseed' oil fatty acids, animal my acids, palm oil fatty acids, hydrogenated fish oil fatty acids and their mixtures and/ or their glycerides such as lard, beef, rapeseed, palm, menhaden, herring, castor oils, etc. Y

,The lubricating oil menstruum may be anyof. the conventionally used mineral, animal, vegetable or synthetic lubricating oils. In general, these lubricating oils should have a viscosity of about 50 to 2000'SUS at 100 F. and

labout 35 to 200 SUS at 210 R, an A.S.T.M. pour point of about +20 to 75 F., a flash point of about 350 to 650 F. and a viscosity index of about 0 'to 60 or higher.

Conventionally refined and treated mineral oil base stocks which are derived from paraflinic, naphthcnic and mixed base crudes and'have the properties listed above are especially useful in preparing the sodium bas lubricating grease compositions.

The synthetic lubricating oils which may also be employed include esters of monobasic acids (e.g. an ester of C Oxo alcohol with C 0x0 acid, an ester of C OX0 alcohol with octanoic acid, etc.), estersof dibasic acids (e.g. di-Z-ethyl hexyl sebacate, di-nonyl adipate, etc.),

esters of glycols (e.g. C Oxo acid diester of tetraethylene glycol, etc.), complex esters (e.g. the complex ester formed by reacting one mol of tetraethylene glycol with two molesof sebacic acid and two moles of Z-ethylhexanol, or the complex ester formed byreacting one" mol of tetraethylene glycol, one mol of adipic acid, one mol of C Oxo alcohol and one mol of C OX0 acid, etc esters of phosphoric acid (e.g. the ester formed by contacting three moles of the mono-methyl ether of ethylene glycol with one mol of phosphorous oxychloride, etc.), halocarbon oils (e.g. the polymer of chlorotrifluoroethylene containing twelve recurring units of chlorotrifluoroethylene), carbonates (e.g. the carbonate formed by reacting C Oxo alcohol with ethyl carbonate to form a half ester and reacting this half ester with tetraethylene glycol), mercaptals (e.g. the mercaptal formed by reacting Z-ethyl hexyl mercaptan with formaldehyde), formals (e.g. the formal forced by reacting C Oxo alcohol with formaldehyde), polyglycol type synthetic oils (e.g. the compounds formed by condensing butyl alcohol with fourteen units of propylene oxide, etc.), or mixtures of the above in any proportions. p

The preparation of the sodium soap thickened greases may be carried out by any of the conventional processes described in sections 11:4 to 11:13 of chapter 11 of Boner, supra. Since the preparation of lubricating greases is not directly related to the present invention, these methods need not be described in detail.

In accordance with one aspect of this invention, a sodium base grease wherein the thickener is prepared from certain glyceride-type fats and oils may be advantageously subjected to high intensity ionizing radiation comprising gamma rays. The saponifiable material used in preparing these greases may be saturated, unsaturated or hydrogenated naturally occurring glyceridetype fats and oils of animal or vegetable nature, such as tallow, hog fat, rapeseed oil, etc. -In general, these greases are prepared by the alkali fusion of the gly'ce'ridetype fat or oil in the presence of the lubricating oil rnenstruum. The amount of alkali metal base, e.g., sodium hydroxide, employed will be in excess of the amount required for saponification of the glycerides. The temperatures employed during alkali fusion will generally be within the range of about 450 to 600 F, preferably about 480 to 570 F.

While the reaction mechanism is not fully understood, it is postulated that the alkali fusion of the glyceride-type fats and oils results in the formation of an alkali metal soap and an alkali metal salt of low molecular weight caaboxylic, :acid. Thus, the grease thickener in these g'reases is believed to be an alkali metal soap-salt com,- plex For the purposes of the invention, the sodium jsoap-salt'complex thickened greases are preferred. In Patent No. 2,265,791, the preparation of such a grease from rapeseed oil as the saponifiable material is T described. v

More specific'ally s odinni.soap salt complex thickened "greases may 'be prepared by slowlyheating rapeseed oil withan excess of alkali in alubricating oil to a tempera [-ture of about "350.to 380 F. to effect saponification. 'The amount ofalkali used is about 75 to 125% in excess, preferably about twice that required to saponify Tithe. rapeseed oil. I ture. is .then' raised to at least-about 425 F. at which temperature hydrogen 'gas evolution commences. The

The temperature of the reactionmixmixture is then heated to and maintained at a temperatur'eof about 450 to 500 F. for about 1, to 4 hours, preferably for about 2 hours. It is believed that during thisheating step the rapeseed oil soap breaks down to some extent to liberate glycerin. The glycerin in turn ,breaksdown to produce acrolein, which is converted .into the alkali metal salt of a low molecular weight acid ,by alkali fusion. Thus, the final product comprises a mixture of C to C fatty acid soaps with sodium acrylate in minor proportions, up to about 1 mol of 1 sodium acrylate per mol of sodium soap of high molecular weight acids.

sodium propionate and the like may also be present.

In general, the sodium base greases will comprise about 3 to 50 wt. percent, preferably about 5 to 35 wt.

Some sodium formate, sodium acetate,

percent, of the thickening agent, i.e. the sodium soap or the sodium soap-salt complex obtained by alkali fusion,

and about 50 to 97 wt. percent, preferably about 65 to 95 wt. percent, of the lubricating oil. The greases may The following example and tables are presented to illustrate the preparation and various characteristics of the improved sodium base greases of the invention.

I EXAMPLE I A numberof sodium base lubricating j g'reases"were i'rradiated by filling one ounce screw-top bottles tothe neck with the lubricating grease, closing the bottle with a plastic screw-top to leave very little air in the container, and thenlowe'ring the bottlesinto the' ceiiter'of a cylindrical cobalt 60 source. The undisturbed radiation intensity of source used to irradiate greases A and B was about 2.2 )(10 roentgens per hour, whereasan undisturbed radiation intensity of about l.74 10 roentgens per hour was used in the irradiation of grease C. All of f the greases were irradiated for 168 hours at a temperature of about 100 F.

The greases had the following formulations:

Mineral lubricating oil, 55 SUS at 210 F. 88.0

The effect of gamma ray irradiation on the above greases is set forth in the following table:

Table Change in Dropping Point F. Micro Penetration, mm./10 Grease Color Odor Before After Change Before 7 "After Lighter--. Less 0dor 500+ 500+ o 79 7s d0 386 390 +4 85 I 88 Lighter- 374 410 +36 203 243 1 No change noticeable since base oil is dark green-black. 2 No change in odor since it was odorless to begin with.

also contain minor proportions of conventional grease additives. More particularly, they may contain oxidation inhibitors (e.g. phenyl alpha-naphthylamine and ditertiary butyl para cresol), metal deactivators, rust inhibitors, dyes, etc.

The irradiation of the sodium base greases may be carried out by a variety of procedures. For example, the radioactive source may be placed in a tank containing the greases to carry out a batch operation or the radioactive source may be placed into a stream of the grease for a continuous or semicontinuous operation. Many obvious modifications of these procedures will be apparent to those skilled in the art. The utilization of radiation emitted by radioactive material will necessitate, ofcourse, adequate radiation shielding means and techniques. Such means and techniques are, however, well known in the art and need not be described here in detail. The irradiation of the sodium base greases may be generally carried out at temperatures within the range of about 20 to 400 F. or higher. In general, the irradiation will be carried out at a temperature of about to 200 F., preferably about 78 to 130 F. and under vacuum or elevated pressures, such asabout 2 to 50 at- .-mosphc e H we one at he. dv s. the

resen r g ess t a ta ay h isstiYsl utililed'at temperature and at atmospheric pressure.

The above data show that physical properties of sodium base lubricating greases can be improved by subjecting the greases to high intensity ionin'ng radiation comprising gamma rays. Greases A and C both showed color improvement after irradiation, while greases 1k and B showed odor improvement. In addition, both greases B and C had higher dropping points following gamma ray irradiation; grease A having already such a high dropping point that no improvements can be measured with conventional methods.

It will be further understood that the invention is not necessarily limited to the specific materials and operating conditions of the foregoing examples. These materials and conditions may be varied within the limits indicated in the general portions of the specification.

What is claimed is: p

1. A method of improving the dropping'point of a lubricating grease consisting essentially of a major 0 proportion of a mineral lubricating oil and a thickening amount of a sodium soap of a carboxylic acid having 12 to 30 carbon atoms per molecule, which comprises ex- Tposing said grease 'to an amount of gamma radiation 'sufiicient to increasdthe droppinglpointof saidlgr'easei'and the range 6f1'0 "t0'3 )2 10 roentgensfandrecover- 5 ing a lubricating grease having an increased dropping FOREIGN PATENTS 154,213 Great Britain Apr. 24, 1922 2. The method of claim 1 wherem 831d sodium soap 665,263 Great Britain Ian. 23 1952 1S Sodlum stearate- 66,034 France Dec. 12, 1955 3. The method of claim 1 wherein the amount of said 5 4 h dditi of No. 1,079,401) gamma radiation is within the range of 10 to 3x10 roentgens. OTHER REFERENCES Mincher: KAPL-731, pp. 3-8, Apr. 2, 1952. Deciass- References Qited in the file of this patent 10 fied Feb. 15, 1955. v: UNITED STATES PATENTS AP $115311 3? Eng. News, Vol. 35, No. 17, page 28, A 2,637,695 McKinley et a1 May 5, 1953 Proceedings of the Second United Nations Interna- 2,719,122 Morway Sept. 27, 1955 tional Conference on the Peaceful Uses of Atomic 2,743,223 McClinton Apr. 24, 1956 Energy, v01. 29, pp. 276-286 (1958). 

1. A METHOD OF IMPROVING THE DROPPING POINT OF A LUBRICATING GREASE CONSISTING ESSENTIALLY OF A MAJOR PROPORTION OF A MINERAL LUBRICATING OIL AND A THICKENING AMOUNT OF A SODIUM SOAP OF A CARBOXYLIC ACID HAVING 12 TO 30 CARBON ATOMS PER MOLECULE, WHICH COMPRISES EXPOSING SAID GREASE TO AN AMOUNT OF GAMMA RADIATION SUFFICIENT TO INCREASE THE DROPPING POINT OF SAID GREASE AND WITHIN THE RANGE OF 10**5 TO 3X10**10 ROENTGENS, AND RECOVERING A LUBRICATING GREASE HAVING AN INCREASED DROPPING POINT. 